Chain: The chain should also be inspected for wear. If you have over 8,000 miles on it, it may be a good idea to get a new one. A broken link could be a race day nightmare if you haven't brought a chain tool and a few extra links.
Bolts: Lastly, make sure your bolts are all tight on all points of weight bearing (stem, handlebars, seat and seat post). This is just to make sure they have started to come loose, which can cause a crash. If your bolts do need to be tightened, be sure to stay within the torque recommendations for each part.
If you're having problems with shifting or the brakes, take the bike to the shop if you aren't sure how to complete these repairs on your own.
Check the Weather
Temperatures and conditions can be quite drastic from morning into the afternoon. When you check the weather, make sure you look at the whole day's forecast by the hour. What was once a sunny morning could turn to an afternoon of rain, and when you're on the bike for six hours, you'll need to be prepared.
Think about what all possibilities are before you pick out your race day clothing.
Pick the Right Race Kit
Having a quality jersey and bib is a must for race day. Although you may be able to get away with old or worn clothing commuting to work or training, on race day it can be a disaster.
After all the hard work you've put in, you don't want to end up with a hole in your shorts at the wrong time or have to sit on a chamois insert that was worn long ago. If you have a favorite kit, by a new one.
If you buy something new, make sure you wear it a few times before the day of the race. You don't want to get out on the road and find out the pair of shorts that looked nice on the hanger has seams in just the wrong spots, or that the jersey fits you a little too snug on the shoulders.
It might also be a good idea to use chamois cream on your insert. Chaffing is common on long rides, and you don't want to end up with a saddle sore. Cream can help reduce the friction between your shorts and the seat, and is particularly useful during long rides like a century.